Pilot-channel protective relaying system



March 10, i942. B, E, LENEHAN PILOT-CHANNEL PROTECTIVE RELAYING SYSTEMFiled sept. 1o, 1940 L e /as INVENTOR er/mrc/E. Lene/m11.

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Patented Mar. l0, 1942 UNlTE STATES FILT-CEANNEL PROTECTIVE RELAYINGSYSTEM Bernard E. Lenehan, Bloomfield, N. J., assignor to WestinghouseCompany, East Pitt of Pennsylvania Electric & Manufacturing sburgh, Pa.,a corporation 28 Claims.

My invention relates to protective relaying systems such as are employedfor protecting transmission-line sections, or other protected electricalapparatus, against faults, and for similar purposes, and it hasparticular relation to such systems utilizing a pilot-channel orcommunicating-channel for obtaining a current from some other point inthe transmission line for assisting in blocking a line-segregating orsecticnalizing operation of a circuit-breaker in the event of atransmission-line fault occurring beyond said other point. Thecommunicating channel may be either a pair of pilot wires, or a tunedhigh-frequency carrier-current circuit, or any other means wherebyintelligence or a signalcurrent-change may be communicated from onepoint to another.

In certain of its aspects, my invention is an improvement over theprotective relaying system which is described and claimed in anapplication of Myron A. Bcstwick, Serial No. 350,658, filed August 3,194), for Pilot-channel protective relaying systems, and also over theprotective relaying system which is described and claimed in anapplication of Shirley L. Goldsborough, Serial No. 356,150, ledSeptember l0, 1940, for Pilotchannel protective relaying systems, bothof said applications being assigned to the Westinghouse Electric &Manufacturing Company.

One of the objects of my invention is to provide a protective relayingsystem utilizing a fault-responsive relay having a fault-responsiveoperating-means which is energized during successive half-cycles of thefault-current, and having two intermittently pulsating restrainingmeansresponsive to alternate half-cycles of the line-currents at oppositeends or terminals of the protected line or apparatus, each of theintermittently pulsating restraining-means having force-pulsationslasting for approximately onehalr cycle of the line-current, withpractically zero-force ericds between said pulsations, and thepulsations of the two restraining-means which are responsive to currentsat opposite ends ci the protected apparatus being substantially 180 outof phase with each other in the event of a fault-current flowing throughthe protected line cr apparatus to some external faulted point. .Afurther object of my invention is to provide a carrier-current relayingsystem of the class just described, in which a single carrier-currentreceiver is utilized, at each relaying point, to respond tocarrier-current transmitters, of the same frequency, at the respectiveends or terminals of a protected line-section, thereby avoidand aline-segregating circuit-breaker ing the trouble and complexity ofhaving transmitters and receivers of different frequencies forsegregating the responses at the respective terminals of the protectedline-section.

A more specific object of my invention is to provide means for producingor transmitting the intermittent force-pulsations during somewhat morethan a half-cycle of the line-current function to which a response ismade, so that these pulsations will overlap each other somewhat whenthere is a through-current passing through the protected line orapparatus, thereby making the protective system less critical of slightphasedisplacements of the current-responses at the respective ends ofthe protected line or apparatus.

With the foregoing and other objects in view, my invention consists inthe apparatus, combinations, systems and methods hereinafter describedand claimed, and illustrated in the accompanying drawing, wherein:

Figure l is a somewhat sirnplied diagrammatic view illustrating apreferred form of embodiment of my invention in the terminal protectiveequipment for one end of a protected transmission-line section;

Fig. 2 is a corresponding view of the corresponding apparatus at theother end of the protected line-section, with certain modificationswhich have been made for the purpose of further illustrating myinvention, although ordinarily the two terminal equipments at therespective ends of the line-section would be identical with each other,in actual service; and

Figs. 3, 4, 5 and 6 are wave-form diagrams illustrating the principlesof operation of the invention.

In Figures 1 and 2, I have shown my invention, by way cf illustration,as being utilized for the protection of a line-section I of athree-phase transmission line. The illustrated line-section 1 extendsbetween a station which is shown in Fig. l, and comprising a bus 8 and aline-segregating circlnt-breaker 9, and another station which is shownin Fig. 2 and which comprises a bus II I2, the circuit-breakers 9 and I2being utilized for disconnecting the protected line-section from otherapparatus represented by the respective buses 8 and l I. Each of thecircuit-breakers 9 and I2 is provided with a trip-circuit I3 which, whenproperly energized, will effect a line-segregating operation of therespective circuit-breaker 9 or I2.

The protective equipments at the two ends of the protected line-sectionare, for the most part,

duplicates of each other, so that a description of one will suice, ingeneral, for the other. Ordinarily, both terminal protective equipmentswill be alike, certain variations being shown in the accompanyingdrawing merely for purposes of illustrating equivalent or alternativeconstructions.

Each terminal protective equipment comprises a bank of line-currenttransformers I5 which will be regarded as looking into the protectedlinesection, thatl is, as responding to currents owing into theline-section from its terminal bus. The line-current transformers areutilized to energize a special phase-sequence means or network which isindicated at HCB, and which is designed to provide a single-phaseoutput-circuit I 6 in which there will be produced or derived analternatingcurrent relaying quantity which is nearly enoughapproximately equally sensitively responsive, in magnitude, to any oneof a plurality of diiierent kinds of faults of equal severity, that is,of equal distances from the relaying points, whether the fault besingle-phase, polyphase, line-to-line or a ground-fault. The particularphase-sequence network HCB which is illustrated in Figs. 1 and 2 is acombined positive and zero phase-sequence network such as is describedand claimed in a Harder Patent No. 2,183,646, granted December 19, 1939,and assigned to the Westinghouse Electric & Manufacturing Company,although I wish my illustration to be construed as being broadly 2trated a saturating iron-core reactor or transformer I'I and a neon lampor other limitedvoltage discharge-tube I8, both connected inparallel-circuit relation to the network-terminals I6, in a manner whichis described and claimed in a Bostwick Patent No. 2,183,587, granted Defcember 19, 1939, and assigned to the Westinghouse Electric &Manufacturing Company, although I am not limited to this particularvoltage-limiting means.

The combined output of the phase-sequence network HCB and thevoltage-limiting means I'I-IB is supplied to a relaying-circuit 25h-2|,to which there is thus applied a single-phase relaying-voltage which,during line-fault conditions, has an approximately (although notabsolutely) xed magnitude, but having a denite timephase relationship tothe line-current at the relaying point, in response to a predeterminedphase-sequence function of the polyphase linecurrent. The wave-form ofthis approximately constant-magnitude relaying voltage in the circuit2Il-2I is approximately sinusoidal, during mild, line-fault conditions,but it is generally quite hat-topped, in its wave-shape, during verysevere fault-conditions on the protected line-section 1.

The limited-voltage output of the relayingcircuit Ell-ZI is utilizedprimarily for two purposes, in accordance with my invention. The

rst use of this relaying voltage is to energize a fault-responsiverelay-operating means, which is illustrated, in Fig. l, as theoperating-coil 22 of a differential relay 23. The relay 23 may be of anydesired type whatsoever, and its illustration, in Fig. 1, is intendedonly to be schematic, and illustrative of the fact that the coil orwinding 22 tends to close the relay-contact 24.

In Fig. 2, the fault-responsive relaying-means which is energized fromthe relaying-circuit 2li-2l is the operating-coil 25 of an auxiliaryfault-detector relay 26 which responds, by closing its relay-contact 27,to energize the operatingwinding Z8 of a differential relay 29 which maybe similar to the differential relay 23 of Fig. l, being utilized toclose its relay-contact 30. In Fig. 2, the operating-coil 28 of thediiierential relay 29 derives its energy from a constantvoltagestation-battery which is represented by the battery-terminals (-4-) and'Ihe second use which is made of the limited relaying-voltage of therelaying-circuit Ztl-2l, in accordance with my invention, is to controlthe operation of the oscillator-tube 32 of a highfrequencycarrier-current transmitter which is indicated, in its entirety, at 33.In accordance with my invention, I desire this carrier-currenttransmitter-control to be efiected in response to a predeterminedfault-magnitude, and approximately in response to alternate half-cyclesof the relaying-voltage which is produced in the relaying-circuit ZIJ-2I. More specifically, I prefer to provide means whereby each of theperiods of energization of the oscillator-tube 32 shall last lorsomewhat longer than a half-cycle of the line-frequency current,although the carriertransmitting periods may be somewhat less than ahalf-cycle of the line-frequency current if the differential relay 23 or2K5-29 is sufliciently sluggish (relatively speaking), in accordancewith the principles of operation which will be subsequently described.

In Figs. l and 2, I have shown an exemplary form oftransmitter-controlling means of the nature just described, and althoughthis means is, in one sense, a preferred means for this purpose, yet ina broader sense, it is to be regarded merely as representative orillustrative of any one of a plurality of different means which could beutilized for the same, or a similar, purpose.

The output of the locally-responsive relayingcircuit 'Z3-EI isillustrated as being applied to a resistor 35, producing therein avoltage-drop which is utilized to energize the shunt-connected primarywinding 36 of a transformer 31 having a secondary winding 38 which isconnected in series with a source of constant unidirectional voltagesuch as the station-battery which is represented by its terminals (-i-)and the series circuit which includes the transformer-secondary 38 alsoincluding a reversely-connected rectier which is represented as adiode-valve 40, and a resistor 4 I. Thus, the plate-circuit of thediodevalve l0 may be traced from the negative battery-terminal throughthe resistor 4I, to a point 42 which is connected to the anode 43 of thediode-valve or rectier 4I). The circuit then continues, from the cathode"I4 of the valve 40, through the transformer-secondary 33, to thepositive battery-terminal (-1-). It will be noted that this diode-valveor rectier-tube 49 is in a non-conducting condition with respect to thestation-battery (-1-) and because the station-battery attempts to passcurrent in the wrong direction therethrough. As a consequence,

2,275,971 the rectifier-tube it operates as a valve which permitscurrent to flow only during positive halfcycles of the voltage inducedin the transformersecondary 33, and only when that induced voltageexceeds the voltage of the station-battery and In the illustratedembodiment of my invention, I also utilize a control-tube i5 which isillustrated as comprising a cathode 46, a grid 47, a screen 48 and aplate or anode lit. As shown in Fig. 1, the control-tube plate 49 isconnected to the positive battery-terminal (-l) through the primarywinding of a transmitter-energizing transformer 52 which is illustratedas an ironcore transformer having, in its magnetic circuit, an air-gap53 for preventing saturation as a result of the direct-currentexcitation thereof. The primary transformer-winding iii is permanentlyshunted by a discharging-resistance 54. In Fig. 2, the air-gap 555 isomitted, and saturation of the transformer i2 is prevented by means of aseries capacitor 5ft' which is connected in series with the primarywinding '5I and is parallel to the resistor 54, so as to exclude thedirect current from the transformer 52.

The screen i8 of the control-tube 65 is connected to the positivebattery-terminal (-i), while the grid il is connected to the point #l2which is connected to the negative battery-terminal through the resistorIii. The cathode it of the control-tube 45 is connected directly to thenegative battery-terminal When the diode-valve or rectier--tube 4i!) isnon-conducting, so that it draws no current through the resistor Iii,the potential of the connecting-point 42, and hence of the control-tubegrid fil, is practically exactly that of the negative battery-terminalbecause the grid 41 carries practically no current at all. Under thesecircumstances, which I shall refer to as the normal operating-condition,the control-tube grid 2i is at the saine potential as its cathode 45, sothat said control-tube is normally conducting current from the positivebattery-terminal (-1-) through the primary transformer-winding 5i, andthence to the plate of the controltube, the circuit being completed fromthe cathode t5 of the control-tube to the negative battery-terminal Theprimary transformer-winding 5i is utilized to magnetize a transformer 52having a secondary winding which is utilized as the equivalent of theB-loattery for the oscillator-tube 32 of the carrier-current transmitter33 which will now be described. The oscillator-tube is illustrated ashaving a cathode 5E, a grid 5l, a screen 58 and a plate or anode 59. Theanode-cathode circuit or plate-circuit of the oscillator-tube 32 isenergized, at periodic intervals, as will be subsequently explained,from the transformer-secondary 55 which serves as an intermittent sourceof direct-current voltage of the proper polarity. This anode-cathodecircuit or slate-circuitof the oscillator-tube 32 may be traced from theplateterminal 6i, through a high-frequency chokecoil 62, to the terminalt3 oi the screen and thence to the terminal M of thetransformer-secondary 5o, and finally to the other terminal t5 thereof,which also constitutes the cathode-terminal of the oscillator-tubesecondary 55 is ley-passed hy a high-frequency by-passing-oapacitor Theoscillator-grid 51 is connected to the cathode *it through agridresistor Gti.

The high-frequency or oscillating-current out- The transformer- 3 put ofthe oscillator-tube 32 is supplied, through a blocking capacitor S9 to atuned circuit 'H which comprises a variometer l2 and three capacitorsi3, and 15. The junction-point 1S between the capacitors 'F4 and i5 isconnected to the cathode-terminal 35 oi the oscillator-tube 32. Oneterminal of the variometer l2 is connected to the oscillator-grid 5T,while the other terminal of the variometer 'i2 is connected, through theblocking capacitor te, to the oscillator-plate 59.

The two capacitors 'it and l' of the tuned circuit ii of the oscillatorare utilized as matched capacitors for energizing a push-pullampliercircuit which is illustrated as comprising two identicalamplifier-tubes il. Each of -the amplifier-tubos 'il is iliustrated ascomprising a cathode it, a grid iii, a screen 8d and a plate iii. Thecathodes iii of the two amplifier-tubes connected to the common terminal76 of the coupling-capacitors iii and l5 through a bias'- ing resistorEach of the ampliiier-grids 19 is connected to its cathode 'it through abiasing resistor 3ft and the previously-mentioned biasing resistor 83,and each amplifier-grid lil is also connected to its associatedcoupling-capacitor M through a blocking-capacitor 555. The plates El ofthe two ampiier-tubes il' are connected to the respective terminals ofthe primary winding Si of a radio-frequency transformer t3. Thetransformer-primary iii has a midpoint-tap Q5 which is connected to thetwo amplifier-screens Eil, and which is coupled to the twoamplifier-cathodes iii through a' blocking-capacitor iii. Energy for theampliiier-tuhes 'li is obtained from the station-battery which has itspositive terminal connected to the midpoint Sii, while its negativeterminal is connected to the junction-point l' between the two couplingcapacitors 'lli and l5.

The output of the radio-frequency transformer 88 is coupled to one ofthe conductors of the protected line-section l' by means of a. secondarywinding 92 of said radio-frequency transformer, one terminal of thesecondary 92 being grounded, and a tap S3 being provided to energize atuned circuit comprising a variometer 94, an adjustable inductance 95and a coupling-capacitor The common point or junction Si between thevariable inductance S5 and the coupling-capacitor 95 is grounded througha choke-coil 9S, while the other terminal of the coupling-capacitor Si@is connected to the line-conductor to which the carrier-currentequipment is coupled, the carrierfrequency currents being substantiallyconnned in this line-conductor by means of a carrier-irequency choke orwave-trap Siti.

In addition to the carrier-current transmitter which has just beendescribed, I also provide a carrier-current receiver which isillustrated as comprising a receiver-tube iti having a cathode |82, agrid H33, a screen EFM and an anode |05. The receiver-tube iili iscoupled to the secondary winding 92 of the radio-frequency transformer#35 by means of a tap liiii. The portion of the transformer-secondary S2between grounded terminal and its tap Mit .is coupled to a ti redreceiver-circuit comprising a variable capacitor im and the primarywinding iii or a couplingtransformer iii. The tuned circuit whenproperly adjusted, is in series resonance, hut the inductance or windingis sleur/.ted by a neon glow protector lamp iii which serves to destroythis series resonance when strong carrier-current signals are received,said neon lamp limiting the voltage across the winding Hi8 to asubstantially predetermined fixed amount, such as approximately 150volts. The coupling-transformer |09 has a secondary winding ||2 which isa part of a tuned circuit comprising an adjustable capacitor H3. Oneterminal of the secondary winding ||2 is connected to the negativebattery-terminal while the other terminal is connected to thereceiver-grid |33 through the grid-capacitor H and the grid-resistor H5,the capacitor I l5 and resistor l5 being connected in shunt relation toeach other.

The receiver-cathode |02 is connected to the negative battery-terminalthrough a potentiometer ||1 which normally biases the grid |53 to asmall negative potential with respect to the cathode |02, so that noplate-current normally flows. The receiver-plate or anode |55 isconnected to the positive battery-terminal through a restraining-windingl IB which, in Fig. 1, is a part of the differential relay 23, andwhich, in Fig. 2, is a part of the differential relay 29. Thereceiver-tube circuits are completed by means of a high-frequencybypass-capacitor which is connected between the plate 05 and the cathode|22, and a connection |2| from the screen |04 to the positivebattery-terminal The operation of the illustrated embodiment of myintermittent transmitter-controlling means will first be described, withreference to the curve-diagrams in Figs. 3 to 6. In Fig. 3, the

datum-line |22 may be taken as the potential appearing at the positivebattery-terminal in Fig. 1 or Fig. 2. This will be the potential of theupper terminal of the secondary winding 33 of thetransmitter-controlling transformer 31. The potential of the bottomterminal of the transformer-secondary 33, which is connected t0 therectifier-cathode 44, is represented in Fig. 3 by the wave-form |23,which is shown as an approximately sine wave-form, although it maycommonly be somewhat nat-topped in its shape. In the time-curve which isrepresented in Fig. 3, the time up to the point |24 is supposed torepresent normal line-conditions when the transmission line 'I iscarrying its full rated load-current, without any fault on thetransmission line. The voltage of the negative battery-terminal isrepresented, in Fig. 3, by the straight line |25. It will be noted thatthe peak-voltage of the transformer-secondary 38, as represented by theline |23, is somewhat smaller than this batteryvoltage |25. During thenon-conducting condition of the rectifier-tube 40, the battery-voltageline |25 also represents the voltage of the control-tube grid 41,representing a condition when the control-tube 45 is conducting currentfrom the battery.

At the point |24 in the time-curve of Fig. 3, it is assumed that a faultoccurs on the transmission line, and that the secondary voltage |23increases to a certain fault-magnitude which is indicated at |23. Itshould be noted, by Way oi explanation, that the voltage-limiting means|8 which is utilized in the local relaying circuit is not absolute inits operation, but permits the relaying voltage to rise very slowlywhile the fault-current is increasing very rapidly. During alternatehalf-cycles of the voltage in the sec'- ondary winding 38, thewinding-voltage |23 adds onto the battery-voltage |25 to make therectifier-cathode 44 still more positive with respect to itsanode-potential which is represented at |25 in Fig. 3. While I haveshown this waveform |23', in Fig. 3, as being a positive half-cycle,extending from the point |24 to the point it is also true that if thevoltage is considered from the standpoint of the conducting-direction ofthe rectifier-tube 4|), this half-cycle of the transformer-voltage |23may be regarded and defined as a negative half-cycle.

During the next half-cycle, the potential of the bottom terminal of thetransformer-secondary 38, which is the potential of the rectifiercathode44, becomes negative with respect to the positive battery-terminalpotential |22, as indicated at |23 in Fig. 3, and at a certain point inthis half-wave, as indicated at |21, the potential |23l of therectifier-cathode 44 becomes negative with respect to the potential |25of the negative battery-terminal with the result that, so long as thiscondition exists, or from the point |21 to the point |28, in Fig. 3,current is flowing from the negative battery-terminal in Fig. l, throughthe resistor 4| to the rectieranode 43, and thence through therectifier-tube 40 to the cathode 44, and through the transformer-winding3B which now serves as a positive sour-ce of potential for therectifier-tube 4l), lorcing current in the charging direction throughthe station-battery represented by the terminals and Fig. 4 shows thecurrent-conditions prevailing in the control-tube 45. The straight lineis the datum-line, representing zero plate-current conditions, while theplate-current of the controltube 45 is indicated at |3| in Fig. 4. At atime IZ'I corresponding to the point |27 in Fig. 3, the control-tubegrid 47 begins to become negative with respect to the cathode 45 whichis at the negative battery-terminal potential |25 in Fig, 3.Consequently, the plate-current |3| begins to fall rapidly to Zero, asindicated at |3| in Fig. (l. When the grid-potential again becomes thesam-e as the control-tube cathode, as at the point |28 in Fig, 3, theplate-current again assumes its normal value as indicated at 3| in Fig.4.

Fig. 5 shows the plate-voltage conditions in the control-tube 45. Thedatum-line |32 is here taken as the voltage of the negativebattery-terminal while the straight line |33 represents the potential ofthe positive battery-terminal which, during the steady-stateconducting-period of the control-tube, is substantially also the voltageof the anode 49 of the control-tube, because under these steady-stateconditions, `there is very little voltage-drop in the primary winding 5|of the oscillator-energizing transformer 52. When the plate-current ofthe control-tube 45 suddenly reduces to zero, as indicated at |3| inFig. 4, the inductance of the primary winding 5| produces a suddenincrement of voltage, which raises the plate-voltage of the control-tubeto a point which is indicated at |34 in Fig. 5, this increase in voltagebeing limited by the resistance 54 which is shunted around the primarywinding 5|. The stored magnetic energy in the winding 5| then commencesto discharge through the resistor 54, producing a sloping portion |35 ofthe platevoltage curve in Fig. 5. When the control-tube again becomesconducting, so that its platecurrent increases to the point |32 in Fig.4, the inductance of the transformer-primary 5| again opposes the suddenchange in current, reducing the plate-potential of the control-tube i5to a value such as Ithat indicated at |35 in Fig. 5. Thereafter, theoscillator-energizing transformer 52 begins to gradually build up itsnormal excitation or magnetization, along a slowly increasing curveindicated at |31 in Fig. 5, which continues until the nextnon-conducting period of the control-tube 45.

The Voltage of the secondary winding 55 of the oscillator-energizingtransformer 52 may be regarded as the difference b-etween the curve|34-|35-|3'6-|31 and the straight-line curve |33, considering the latteras the datum-line for said secondary voltage. The polarities of theconnections between the secondary winding 55 and the oscillator-tubel 32are such that a positive plate-voltage is applied to said tube duringthe period represented by the curve |31 in Fig. 5, that is, when thecontrol-tube 45 is conducting current after a brief period ofnon-conduction. During this period |31 in Fig. 5, a diminishingplate-voltage is being applied lto the oscillatortube 32, and Fig. 6shows the oscillations |38 which are produced during this periody thefrequency of the oscillations |38 being made far too low, in Fig. 6, inorder to be able to show the wave-form at all.

It will be noted, from the foregoing explanation, that I utilize only aportion of alternate half-cycles of the locally-responsiverelayingvoltage of the circuit 20--2I to render the control-tube 45non-conducting, as indicated by the time-period |21- |28 in Fig. 3, thetime-period 12T-I3 I" in Fig. 4, and the plate-voltage curveportion |35in Fig. 5. Inasmuch as this timeperiod exists for less than one-half ofa cycle of the line-frequency current, the interveningoscillating-periods |31 or |38 of Figs. 5 and 6 must each last forsomewhat longer than one-half of a cycle of the line-frequency current.

It should be lnentioned that the shortness of the non-conducting periodsof the control-tube 45 has been somewhat exaggerated in Figs. 3, 4 and5, which means also that the length of the oscillator-operating periods|31 and |35 has been exaggerated in Figs. and 6, although I am notlimited to any precise period. This is because the `fault-currentwave-form |23-| 23 has been shown in Fig. 3 as a substantiallysinusoidal wave, whereas, in actual fact, it is a considerablyiiattopped wave, which would shorten the lost-time interval between thebeginning of the half-wave |26 in Fig. 3 and the point |21 when theinstantaneous value of transformer-voltage becomes equal to thebattery-Voltage |25.

In order for the oscillator-energizing transformer to operate in themanner abovedescribed, it is only necessary that it should be sodesigned that its time-constant, or the timeconstant of its primary andsecondary circuits, should be such that the transformer would slowlydischarge and charge, or give up its iiux and increase its ilux, in themanner approximately as indicated at |35 and |31, respectively, in Fig.5, without approaching too closely to its steady-state flux-condition|53 by the end of the oscillator-energizing period |31.

Considering the operation of my system from the standpoint of theresponse of the differential relays 23 and 25, it will be noted that therelay-contacts 24 and 55, respectively, are utilized to energize thetripping circuit 3 at the associated end of the line-section, so as toeffect a circuit-interrupting operation of the circuitbreaker. As iscustomary in such tripping circuits, an auxiliary relay |45 is alsoutilized, having its operating coil in series with its tripping circuitI3, and having relay-contacts IM which bypass the more delicatedifferential-relay contacts 24 and 35, respectively.

It is apparent, therefore, that, whenever either one of the differentialrelays 23 or 25 responds, it effects a tripping-operation of itsassociated circuit-breaker 9 or I2, as the case may be. It is essential,therefore, that the differential relays should not respond except duringconditions when there is a current of fault-magnitude on thetransmission line.

It is to be noted, also, that an initiation of carrier-currenttransmission is necessary before the differential relays 23 and 29 canreceive any electro-responsive restraint (as distinguished from thenormal biasing means which may be either a spring or, as illustrated,gravity). lIhe initiation of carrier-current transmission is ensitiveiyresponsive to any increase in the flattopped voltage-output of thetransmitter-controlling transformer 31 over and above the constantvoltage of the station-battery (-i-) and as will be understood from theexplanation already given in connection with Fig. 3.

As a result of the foregoing considerations, it follows that thedifferential relays 23 and 29 cannot be permitted to respond, by closingtheir contacts 25 or 35, during line-current conditions or magnitudeswhich are less severe than the magnitude which initiates the operationof the carrier-current transmitter 33.

In the case of Fig. 1, where the operating coil 22 of the differentialrelay 23 is energized directly from the locally-responsiverelaying-circuit lid-ZL it is necessary for this relay to be lesssensitive, to fault-current magnitudes of the relaying-voltage suppliedby the relayingcircuit 2li-2|, than the transmitter-starting means whichis under the control of the transformer 31 in cooperation with thestationbattery and In other words, without any current in therestraint-winding H5 oi the differential relay 23, this relay must notpick up its movable contact member until the relaying-voltage in thecircuit til-2| increases to a Value higher than that which is necessaryto initiate carrier-current transmission under the conditions explainedin connection with Figs. 3 to 6.

In the case of the differential relay 25 which is shown in Fig. 2, theconditions are somewhat different, because of the presence of theauxiliary relay 25 which is responsive to the current in thelocally-responsive relaying-circuit 26-2L In this case, the differencein sensitivity or selectivity, as to diierent severities offault-conditions, is 'obtained in the auxiliary relay 26 by adjusting itso that it responds less sensitively, to increases in therelaying-voltage of the circuit Eil-2|, than the transmitter-initiatingapparatus associated with the transformer 31, so that the relay 2S willnot pick up until the attainment of magnitudes higher than thevoltage-magnitude necessary to initiate carrier-current transmission, orif an extremely high voltage-magnitude is very quickly attained in therelaying-circuit 2li-2|, the auxiliary relay 26 should respond a triflemore sluggishly, or certainly not materially faster, than thetubecontrolled carrier-initiating means.

The underlying consideration, of course, is to make sure thatcarrier-current is being transmitted at least as soon as the time whenthe differential relay 23 or 29, in Figs. 1 or 2, would be ready to pickup its tripping-circuit contacts in the absence of the restraint whichis applied to the restraining winding ||8 through the medium ofcarrier-current transmission and reception, or if there is any delay inthe initiation of carriercarrier-current transmission at the end Wherefault-current magnitudes do not exist, with the result that trippingwill occur during the rst half-cycle when the restraint- Jinding H3 isnot energized.

In the particular half-Wave-responsive transmitter-initiating mechanismwhich I have illustrated, in connection With the apparatus includedbetween the transmitter-controlling transformer 3'! and theoscillator-energizing transformer 52, there may be a delay ofapproximately a halfcycle of the line-current, or even more, beforecarrier-current transmission will be rst initiated, if, as illustratedin Fig. 3, a fault occurs, as at the moment Ulli, when a half-cycle ofthe wrong polarity E23 is about to commence. Under such circumstances,it is necessary to make sure that the diiferential relay, such as therelay 23 in Fig. l, shall not respond prematurely, beforecarrier-current can be initiated at either end of the protectedline-section. This may be accomplished, either` by the inherentsluggishness of the differential relay t3, or by the addition ofsuitable time-delay means, such as a short-circuited coil M3 on themagnetic circuit of the operating-coil 22, to prevent a prematureresponse of said relay.

In Fig. 2, however, I have indicated the use of a positive means orsafeguard for making sure that the operating-Winding 28 of thedifferential relay 29 cannot become energized before the rst half-cycleduring which carrier-current is transmitted at the relaying station, sothat the response of the differential relay 29 will not, in any event,take place before the next half-cycle after that. Any suitable means maybe utilized for the purpose just stated, preferably a means Which isresponsive to the same voltage which initiates carrier-currenttransmission.

In Fig. 2, the secondary-Winding voltage of the oscillator-energizingtransformer 52 is tapped olf, as indicated at M and itt, and utilized inthe control of a cold-cathode glow-discharge tube 47 having a cathodeU38, a control-grid M9 and an anode EEG. The cold-cathode tube It? isincluded in series-circuit relation to the operating Winding 23 of thedifferential relay 29 in Fig. 2, so that the current tends to flow, fromthe positive battery-terminal through the auxiliary relay-contact '2land the coil E28, into the anode l5@ of the tube till, and thence fromthe cathode It@ to the negative battery-terminal The characteristic ofthe cold-cathode tube Uil (Fig. 2) is such that, when impressed with apredetermined anode-potential, such as the potential of thestation-battery (-5-) and it Will not begin to conduct any materialamount of electricity until its grid lili) has been raised to apredetermined positive potential with respect to the cathode Hi8, thetube-characteristics being such that, once the tube has been brokendown, that is, once the tube has commenced to carry current, it willthereafter continue to carry current independently of the grid-potential(Within reasonable limits) as long as the predetermined plate-voltagecontinues to be applied to the tube. The cold-cathode glow-dischargetube Uil thus operates as a means for making sure that the operatingcoil ZEE of the tripping relay 29 is not energized prior to commencementof carrier-current transmission on alternate half-cycles at the relayingstation at which the tripping relay 2@ is located. Of course, it will beobvious that, instead of utilizing all of the voltage of thepositivehalf-Waves of the transformer-secondary 5?; to control thepotential of the grid i129, a small portion of such voltage could betapped off, as by means of a potentiometer or other Voltage-dividingmeans, as Will be wcll understood by those skilled in the art.

While I have illustrated my invention in connection with the protectionof a section of a transmission line, and While I have illustrated onlytwo slightly different forms of embodiment thereof, I Wish it to beunderstood that my invention, at least in its broader aspects, isapplicable to the protection of other electrical apparatus as well, andthat it isV susceptible of considerable alteration in regard to itsprecise form of embodiment and in its range of equivalents. I desire,therefore, that the appended claims shall be accorded the broadestconstruction consistent with their language.

I claim as my invention:

l. The combination, with an alternating-current transmission-linesection to be protected, and line-segregating circuit-interrupting meansfor disconnecting the line from other apparatus, ofline-fault-responsive relaying-means for actuating said line-segregatingcircuit-interrupting means so as to eifect a disconnecting operation;said line-fault-responsive relaying-means being of a type which utilizesa current obtained from some other point in the transmission line forassisting in blocking a line-segregating operation in the event of atransmission-line fault occurring beyond said other point; characterizedby said line-fault-responsive relaying-means includingelectro-responsive relaying-means at the relaying point for effecting apredetermined control over the line-segregating circuit-interruptingmeans; said electro-responsive relayingmeans having anelectro-responsive restraining means for developing a restraining force,and an electro-responsive operating means for developing an operativeforce which is effective to quickly cause the actuation of theelectro-responsive relaying-means in the absence of said restrainingforce; means operative,A when predeterininedly energized, tosubstantially continuously energize said electro-responsive operatingmeans; means responsive approximately to alternate half-cycles of aline-current function at the relaying point for energizing saidelectro-responsive restraining means approximately during alternatehalicycles of said line-current function at the relaying point; andcommunicating-channel means responsive approximately to alternatehalf-cycles of a corresponding line-current function at said other pointfor energizing said electro-responsive restraining means of theelectro-responsive relaying-means at the relaying point approximatelyduring alternate half-cycles of said line-current function at said otherpoint; the approximate half-cycles during which said restraining meansis energized in response to line-currents at the relaying point and atsaid other point, respectively, being approximately intime-phase-opposition with respect to each other, so as to alternate, inthe event of a transmission-line fault occurring beyond said otherpoint.

2. The invention as defined in claim l, characterized by each of theapproximate half-cycles of energization of the restraining means inresponse to the line-currents at the relaying point and at said otherpoint, respectively, being of slightly longer duration than onehalf-cycle of the line-current so as to provide a certain predeterminedamount oi overlapping of the approximate half -cycles ofrestraining-means energization in the event of a transmission-line faultoccurring beyond said other point.

3. The invention as defined in claim l, characterized by saidelectro-responsive relayingmeans including means for insuring theprevention of the eifectuation of the aforesaid predetermined controlover theline-segregating circuit-interrupting means prior to the firstapproximate half-cycle of restraining-means energization which iseffectua'ted in response to halfcycles of the line-current function atthe relaying point after the occurrence of predetermined line-faultconditions.

4. The combination, With an alternating-current transmission-linesection to be protected, and line-segregating circuit-interrupting meansfor disconnecting the line from other apparatus, ofline-fault-responsive relaying-means for actuating said line-segregatingcircuit-interrupting means so as to effect a disconnecting operation;said line-fault-responsive relaying-means being of a type which utilizesa current obtained from some other point in the transmission line forassisting in blocking a line-segregating operation in the event of atransmission-line fault occurring beyond said other point; characterizedby said line-fault-responsive relaying-means includingelectro-responsive relaying-means at the relaying point for effecting apredetermined control over the line-segregating circuit-interruptingmeans; said electro-responsive relaying means having anelectro-responsive restraining means for developing a restraining force,and an electro-responsive operating means for developing an operativeforce which is effective to quickly cause the actuation of theelectro-responsive relaying-means in the absence of said restrainingforce; means responsive to the attainment of a predetermined magnitudeand approximately to alternate halfcycles of a line-current function atthe relaying point for initiating an intermittent energization of saidelectro-responsive restraining means approximately during alternatehalf-cycles of said line-current function at the relaying point; meansoperative not materially prior to the lastmentioned means for initiatinga substantially continuous energization of said electro-responsiveoperating means; and communicating-channel means responsive to theattainment of a predetermined magnitude and approximately to alternatehalf-cycles of a corresponding line-current function at said other pointfor energizing said electro-responsive restraining means of theelectro-responsive relaying-means at the relaying point approximatelyduring alternate halfcycles of said line-current function at said otherpoint; the approximate half-cycles during which said restraining meansis energized in response to line-current at the relaying point and atsaid other point, respectively, being approximately intime-phase-opposition with respect to each other, so as to alternate, inthe event of a transmissionline fault occurring beyond said other point.

5. The combination, with an alternating-current transmission-linesection to be protected, and line-segregating circuit-interrupting meansfor disconnecting the line from other apparatus, ofline-fault-responsive relaying-means for actuating said line-segregatingcircuit-interrupting means so as to effect a disconnecting operation;said line-fault-responsive relaying-means being of a type Which utilizesa current obtained from Some other point in the transmission line forassisting in blocking a line-segregatng operation in the event of atransmission-line fault occurring beyond said other point; characterizedby said line-fault-responsive relaying-means includingelectro-responsive relaying-means at the relaying point for effecting apredetermined control over the line-segregating circuit-interruptingmeans; said electro-responsive relaying-means having anelectro-responsive restraining means for developing a restraining force,and an electroresponsive operating means for developing an operativeforce which is effective to quickly cause the actuation of theelectro-responsive relayingmeans in the absence of said restrainingforce; means sensitively responsive to the attainment of a predeterminedmagnitude and approximately to alternate half-cycles of a line-currentfunction at the relaying point for initiating an intermittentenergization of said electro-responsive restraining means approximatelyduring alternate half-cycles of said line-current function at therelaying point; communicating-channel means sensitively responsive tothe attainment of a predetermined magnitude and approximately toalternate half-cycles of a corresponding line-current function at saidother point for energizing said electro-responsive restraining means ofthe electro-responsive relaying-means at the relaying pointapproximately during alternate halfcycles of said line-current functionat said othel` point; the approximate half-cycles during which saidrestraining means is energized in response to line-currents at therelaying point and at said other point, respectively, beingapproximately in time-phase-opposition with respect to each other, so asto alternate, in the event of a transmissionline fault occurring beyondsaid other point; and less sensitive magnitude-responsive meansresponsive to successive half-cycles of said linecurrent function at therelaying point for initiating a substantially continuous energization ofsaid electro-responsive operating means.

6. The combination, with an alternating-current transmission-linesection to be protected, and line-segregating circuit-interrupting meansfor disconnecting the line from other apparatus, ofline-fault-responsive relaying-means for actuating said line-segregatingcircuit-interrupting means so as to effect a disconnecting operation;said line-fault-responsive relaying-means being of a type which utilizesa current obtained from some other point in the transmission line forassisting in blocking a line-segregating operation in the event of atransmission-line fault occurring beyond said other point; characterizedby said line-fault-responsive relaying-means includingelectro-responsive relaying means at the relaying point for effecting apredetermined control over the line-segregating circuit-interruptingmeans; said electro-responsive relaying-means having anelectro-responsive restraining means i performing an operation necessaryto an initiation of a substantially continuous energization of saidelectro-responsive operating means; and communicating-channel meansresponsive to the attainment of a predetermined magnitude andapproximately to alternate half-cycles of a corresponding line-currentfunction at said other point for energizing said electro-responsiverestraining means of the electro-responsive relaying-means at therelaying point approximately during alternate half-cycles of saidline-current function ai; said other point; the approximate half-cyclesduring which said restraining means is energized in response toline-currents at the relaying point and at said other point,respectively, being approximately in time-phase-opposition With respectto each other, so as to alternate, in the event of a transmission-linefault occurring beyond said other point.

7. The combination, with an alternating-current transmission-linesection to be protected, and line-segregating circuit-interrupting meansfor disconnecting the line from other apparatus, ofline-fault-responsive relaying-means for actuating said line-segregatingcircuit-interrupting means so as to eect a disconnecting operation; saidline-fault-responsive relaying-means being of a type which utilizes acurrent obtained from some other point in the transmission line forassisting in blocking a line-segregating operation in the event of atransmission-line fault occurring beyond said c-ther point;characterized by said line-faudt-responsive relaying-means includingelectro-responsive relaying-means at the relaying point for effecting apredetermined control over the line-segregating circuit-interruptingmeans; said electro-responsive relaying-means having anelectro-responsive restraining means for developing a restraining force,and an electroresponsive operating means for developing an operativeforce which is effective to quickly cause the actuation of theelectro-responsive relayingmeans in the absence of said restrainingforce; means operative, when predeterminedly energized, to substantiallycontinuously energize said electro-responsive operating means; means forproviding a communicating channel between said relaying point and saidother point; means responsive approximately to alternate half-cycles ofa line-current functio-n at the relaying point for causinghigh-frequency current of a predetermined high frequency to be fed intothe communicating channel approximately during alternate half-cycles ofsaid line-current function at the relaying point; means responsiveapproximately to alternate half-cycles of a corresponding line-currentfunction at said other point for causing high-frequency current of saidpredetermined high frequency to be fed into the communicating channelapproximately during alternate half-cycles of said line-current functionat said other point; the approximate half-cycles during which saidrestraining means is energized in response to line-currents at therelaying point and at said other point, respectively, beingapproximately in time-phase-opposition with respect to each other, so asto alternate, in the event of a transmission-line fault occurring beyondsaid other point; and attuned receivingmeans at the relaying point forenergizing said electro-responsive restraining means in response tohigh-frequency current of said predetermined high frequency in thecommunicating channel.

8. The invention as defined in claim 7, characterized by each of theapproximate half-cycles of high-frequency current-feeding into thecommunicating channel in response to the line-currents at. the relayingpoint and at said other point, respectively, being of slightly longerduration than one half-cycle of the line-current so as to provide acertain predetermined amount of overlapping of the approximatehalf-cycles of said currents fed into the communicating channel in theevent of a transmission-line fault occurring beyond said other point.

9. The invention as defined in claim 5, characterized by saidelectro-responsive relayingmeans including means for insuring theprevention of the eifectuation of the aforesaid predetermined controlover the line-segregating circuitinterrupting means prior to the rstapproximate half-cycle period during which high-frequency current is fedinto the communicating channel in response to half-cycles of theline-current function at the relaying point after the occurrence ofpredetermined line-fault conditions.

l0. The combination, with an alternating-current transmission-linesection to be protected, and line-segregating circuit-interrupting meansfor disconnecting the line from other apparatus, ofline-fault-responsive relaying-means for actuating said line-segregatingcircuit-interrupting means so as to effect a disconnecting operation;said line-fault-responsive relaying-means being of a type which utilizesa current obtained from some other point in the transmission line forassisting in blocking a, line-segregating operation in the event of atransmission-line fault occurring beyond said other point; characterizedby said line-fault-responsive relaying-means includingelectro-responsive relaying-means at the rclaying point for effecting apredetermined control over the line-segregating circuit-interruptingmeans; said electro-responsive relayingmeans having anelectro-responsive restraining means for developing a restraining force,and an electro-responsive operating means for developing an operativeforce Which is effective to quickly cause the actuation of theelectro-responsive relaying-means in the absence of said restrainingforce; means for providing a communicating channel between said relayingpoint and said other point; means responsive to the attainment of apredetermined magnitude and approximately to alternate half-cycles of aline-current function at the relaying point for initiating an in-feedingof high-frequency current of a predetermined high frequency into thecommunicating channel approximately during alternate half-cycles of saidline-current function at the relaying point; means operative notmaterially prior to the last-mentioned means for initiating asubstantially continuous energization of said electro-responsiveoperating means; means responsive to the attainment of a predeterminedmagnitude and approximately to alternate half-cycles of a correspondingline-current function at said other point for initiating an in-feedingof high-frequency current of said predetermined high frequency into thecommunicating channel approximately during alternate half-cycles of saidline-current function at said other point; the approximate half-cyclesduring which said restraining means is energized in response tolinecurrents at the relaying point and at said other point,respectively, being approximately in timephase-opposition with respectto each other, so as to alternate, in the event of a transmissionlinefault occurring beyond said other point; and attuned receiving-means atthe relaying point for energizing said electro-responsive restrainingmeans in response to high-frequency current of said predetermined highfrequency in the communicating channel.

11. The combination, with an alternating-current transmission-linesection to be protected, and line-segregating circuit-interrupting meansfor disconnecting the line from other apparatus, ofline-fault-responsive relaying-means for actuating said line-segregatingcircuit-interrupting means so as to eifect a disconnecting operation;said line-fault-responsive relaying-means being of a type which utilizesa current obtained from some other point in the transmission line forassisting in blocking a line-segregating operation in the event of atransmission-line fault occurring beyond said other point; characterizedby said line-fault-responsive relaying-means includingelectro-responsive relaying-means at the relaying point for effecting apredetermined control over the line-segregating circuit-interruptingmeans; said electro-responsive relayingmeans having anelectro-responsive restraining means for developing a restraining force,and an electro-responsive operating means for developing an operativeforce which is effective to quickly cause the actuation of theelectro-responsive relaying-means in the absence of said restrainingforce; means for providing a communicating channel between said relayingpoint and said other point; means sensitively responsive to theattainment of a predetermined magnitude and approximately to alternatehalf-cycles of a line-current function at the relaying point forinitiating an in-feeding of high frequency current of a predeterminedhigh frequency into the communicating channel approximately duringalternate half-cycles of said line-current function at the relayingpoint and for substantially simultaneously performing an operationnecessary to an initiation of a substantially continuous energization ofsaid electro-responsive operating means; means sensitively responsive tothe attainment of a predetermined magnitude and approximately toalternate half-cycles of a corresponding line-current function at saidother point for initiating an in-feeding of high-frequency current ofsaid predetermined high frequency into the communicating channelapproximately during alternate half-cycles of said linecurrent functionat said other point; the approximate half-cycles during which saidrestraining means is energized in response to line-currents at therelaying point and at said other point. respectively, beingapproximately in time-phaseopposition with respect to each other, so asto alternate, in the event of a transmission-line fault occurring beyondsaid other point; less sensitive magnitude-responsive means responsiveto successive half-cycles of said line-current function at the relayingpoint for initiating a substantially continuous energization of saidelectro-responsive operating means; and attuned receiving-means at therelaying point for energizing said electro-responsive restraining meansin response to high-frequency current of said predetermined highfrequency in the communicating channel.

12. The combination, with an alternating-current transmission-linesection to be protected, and line-segregating circuit-interrupting meansfor disconnecting the line from other apparatus, ofline-fault-responsive relaying-means for actuating said line-segregatingcircuit-interrupting means so as to effect a disconnecting operation;

said line-fault-responsive relaying-means being of a type which utilizesa current obtained from some other point in the transmission line forassisting in blocking a line-segregating operation in the event of atransmission-line fault occurring beyond said other point; characterizedby said line-fault-responsive relaying-means includingelectro-responsive relaying-means at the relaying point for eifecting apredetermined control over the line-segregating circuit-interruptingmeans; said electro-responsive relaying-means having anelectro-responsive restraining means for developing a restraining force,and an electro-responsive operating means for developing an operativeforce which is eiiective to quickly cause the actuation of theelectro-responsive relaying-means in the absence of said restrainingforce; means for providing a communicating channel between said relayingpoint and said other point; means responsive to the attainment of apredetermined magnitude and approximately to alternate half-cycles of aline-current function at the relaying point for initiating an infeedingof high-frequency current of a predetermined high frequency into thecommunicating channel approximately during alternate halfcycles of saidline-current function at the relaying point and for substantiallysimultaneously performing an operation necessary to an initiation of asubstantially continuous energization of said electro-responsiveoperating means; means responsive to the attainment of a predeterminedmagnitude and approximately to alternate half-cycles of a correspondinglinecurrent function at said other point for initiating an in-feeding ofhigh-frequency current of said predetermined high frequency into thecommunicating channel approximately during alternate half-cycles of saidline-current function at said other point; the approximate half-cyclesduring which said restraining means is energized in response toline-currents at the relaying point and at said other point,respectively, being approximately in time-phase-opposition with respectto each other, so as to alternate, in the event of a transmission-linefault occurring beyond said other point; and attuned receivingmeans atthe relaying point for energizing said electro-responsive restrainingmeans in response to high-frequency current of said predetermined highfrequency in the communicating channel.

13. The combination, with an alternatingcurrent electrical apparatus tobe protected, said apparatus having a first terminal where currentnormally enters the apparatus and a second terminal where currentnormally leaves the apparatus, under predetermined power-flowconditions, of fault-responsive relaying-means, means responsiveapproximately to alternate half-cycles of a predeterminedalternating-current function of current in one of said terminals forproducing a first intermittently pulsating restraining force havingforce-periods each lasting for approximately a half-cycle, alternatingwith substantially no-force periods lasting for the remaining timesbetween alternate halfcycles of the current in the associated terminal,half-cycles of a corresponding alternating-current function of currentin the other terminal for producing a second intermittently pulsatingrestraining force having force-periods each lasting for approximately ahalf-cycle, alternating with substantially no-force periods lasting forthe remaining times between alternate halfcycles of the current in theassociated terminal,

the pulsations of said first and second restraining forces beingapproximately in phase-opposition to each other when fault current isflowing through the protected apparatus to some iaulted point outside ofthe apparatus, and faultresponsive relay-operating means for producing asubstantially continuous operating force effective, in less thanone-half of a cycle, under fault conditions, to cause a predeterminedrelayresponse when both of said restraining forces have predeterminedsubstantially noforce periods during a predetermined time-interval.

14. The invention as dei-ined in claim 13, characterized by the factthat both of said intermittently pulsating restraining forces are of anapproximately limited magnitude not sensitively variable in response tothe magnitudes of the currents in the respective terminals of theprotected apparatus.

l5. The invention as deiined in claim 13, characterized by the iact thatthe pulsations of each of the restraining forces are each oi slightlylonger duration than one half-cycle of the current in its associatedterminal so as to provide a certain predetermined amount of overlappingwhen fault-current is flowing through the protected apparatus to somefaulted point outside of the apparatus.

16. The combination, with an alternating-current electrical apparatus tobe protected, said apparatus having a iirst terminal Where currentnormally enters the apparatus and a second terminal Where currentnormally leaves the apparatus, under predetermined power-flowconditions, of fault-responsive relaying-means, means responsivesensitively to an alternating current of fault-magnitude derived fromone of said terminals for initiating the production or a iirstintermittently pulsating restraining force and for causing thepulsations of said first restraining force to be in time-phase response,in some manner, to the alternations of said current derived from itsassociated terminal, means responsive sensitively to an alternatingcurrent of fault-magnitude derived from the other terminal forinitiating the production of a second intermittently pulsatingrestraining force and for causing the pulsations of said second .restraining force to be in time-phase response, in some manner, to thealternations of said current derived from its associated terminal, eachof said restraining forces having force-periods each lasting forapproximately a half-cycle, alternating with substantially no-forceperiods lasting for the remaining times between alternate half-cycles ofthe current in the associated terminal, the pulsations of said rst andsecond restraining forces being approximately in phaseopposition to eachother when fault-current is ilowing through the protected apparatus tosome iaulted point outside of the apparatus, and means responsive, insome measure, to the same derived current as one of saidrestraining-forceinitiating means, and operative subsequently thereto,for initiating a substantially continuous operating force effective, inless than one--half of a cycle, to cause a predetermined relay-re spensewhen both of said restraining forces have predetermined substantiallyvno-force periods during a predetermined time-interval.

17. The invention as defined in claim i6, characterized by the fact thatboth of said intermittently pulsating restraining forces are of anapproximately limited magnitude not sensitively variable in response tothe magnitudes of the currents in the respective terminals of theprotected apparatus.

18. The invention as defined in claim 16, charf acterized by the factthat the operating and restraining forces are of an approximatelylimited magnitude not sensitively variable in response to the magnitudesof the alternating currents by which they are controlled.

19. The invention as defined in claim 16, characterized by the fact thatthe pulsations of each of the restraining forces are each of slightlylonger duration than one half-cycle of the current in its associatedterminal so as to provide a certain predetermined amount of overlappingwhen fault-current is flowing through the protected apparatus to somefaulted point outside of the apparatus.

20. The combination, with an alternating-current electrical apparatus tobe protected, said apparatus having a rst terminal Where currentnormally enters the apparatus and a second terminal where `currentnormally leaves the apparatus, under predetermined power-flowconditions, of fault-responsive relaying-means, means responsivesensitively to an alternating current of lfault-magnitude derived fromone of said terminals for initiating the production of a i'lrstintermittently pulsating restraining force and for causing thepulsations of said first restraining force to be in time-phase response,in some manner, to the alternations of said current derived from .itsassociated terminal, means responsive sensitively to an alternatingcurrent of faultmagnitude derived from the other terminal for initiatingthe production of a second intermittently pulsating restraining forceand for causing the pulsations of said second restraining force to be intime-phase response, in some manner, to the alternations of said currentderived from its associated terminal, each of said restraining forceshaving force-periods each lasting for approximately a half-cycle,alternating with substantially no-force periods lasting for theremaining times between alternate half-cycles of the current in theassociated terminal, the pulsations of said rst and second restrainingforces being approximately in phase-opposition to each other whenfault-current is owing through the protected apparatus to some faultedpoint out* side of the apparatus, fault-responsive relayoperating meansfor producing a substantially continuous operating force effective, inless than one-half of a cycle, to Acause a predetermined relay-responsewhen both of said restraining forces have predetermined substantiallyno-force periods during a predetermined time-interval, and means forinsuring the delay of the effective application of said operating-meanswhich causes the predetermined relay-response until approximately thebeginning of one of the force-periods of one of said intermittentlypulsating restraining forces.

2l. The invention as deiined in claim 20, characterized by the fact thatboth of said intermittently pulsating restraining forces are of anapproximately limited magnitude not sensitively variable in response tothe magnitudes of the currents in the respective terminals of theprotected apparatus.

22. The invention as dened in claim 210, characterized by the fact thatthe pulsations of each of the restraining forces are each of slightlylonger duration than one half-cycle of the current in its associatedterminal so as to provide a certain predetermined amount of overlappingwhen fault-current is flowing through the protected apparatus to somefaulted point outside of the apparatus.

23. The combination, with an alternating-current electrical apparatus tobe protected, said apparatus having a first terminal where currentnormally enters the apparatus and a second terminal where currentnormally leaves the apparatus, under predetermined power-ow conditions,of fault-responsive relaying-means, means responsive sensitively to analternating current of fault-magnitude derived from one of saidterminals for initiating the production of a first intermittentlypulsating restraining force and for causing the pulsations of said firstrestraining force to be in time-phase response, in some manner, to thealternations of said current derived from its associated terminal, meansresponsive sensitively to an alternating current of faultmagnitudederived from the other terminal for initiating the production of asecond intermittently pulsating restraining force and for causing thepulsations of said second restraining force to be in time-phaseresponse, in some manner, to the alternations of said current derivedfrom its associated terminal, each of said restraining forces havingforce-periods each lasting for approximately a half-cycle, alternatingwith substantially no-force periods lasting for the remaining timesbetween alternate half-cycles of the current in the associated terminal,the pulsations of said rst and second restraining forces beingapproximately in phase-opposition to each other when fault-current isflowing through the protected apparatus to some faulted point outside ofthe apparatus, and less sensitive magnituderesponsive means responsive,in some measure, to successive half-cycles of one of said derivedcurrents for initiating a substantially continuous operating forceeiective, in less than one-half of a cycle, to cause a predeterminedrelay-response when both of said restraining forces have predeterminedsubstantially no-force periods during a predetermined time-interval.

24. The invention as dened in yclaim 23, characterized by the fact thatboth of said intermittently pulsating restraining forces are of anapproximately limited magnitude not sensitively variable in response tothe magnitudes of the currents in the respective terminals of theprotected apparatus.

25. The invention as dened in claim 23, characterized by the fact thatthe operating and restraining forces are of an approximately limitedmagnitude not sensitively variable in response to the magnitudes of thealternating-currents by which they are controlled.

26. The invention as dened in claim 23, characterized by the fact thatthe pulsations of each of the restraining forces are each of slightlylonger duration than one half-cycle of the current in its associatedterminal so as to provide a certain predetermined amount of overlappingwhen fault-current is flowing through the protected apparatus to somefaulted point outside of the apparatus.

2V?. The invention as defined in claim '7, characterized by each of saidmeans for causing the feeding of high-frequency current comprising ahigh-frequency oscillator-tube, and said line-current functions at therelaying and other point each comprising a source of relativelylow-frequency control-current for controlling its associatedoscillator-tube, the operative controlmeans between each control-currentand its controlled oscillator-tube comprising an oscillatorenergizingtransformer comprising an iron-core magnetic circuit, a secondarywinding yconnected as a plate-voltage source for said oscillator-tube,and a primary winding, a primary resistor shunting said primary winding,means serially including said primary resistor, a source ofunidirectional voltage and a control-tube for energizing said primarywinding, and control-means responsive, in some manner, to successivehalf-waves of said low-frequency control-current for alternatelyrendering said control-tube conducting and substantially non-conducting,at least under fault-conditions of the transmission-line, thetime-constant of the transformer being such that it will continue tochange its flux throughout all of each of its discharge-periods.

28. The invention as defined in claim 7, characterized by each of saidmeans for causing the feeding of high-frequency current comprising ahigh-frequency oscillator-tube, and said line-current functions at therelaying and other point each comprising a source of relativelylow-frequency control-current for controlling its associatedoscillator-tube, the operative controlmeans between each control-currentand its controlled oscillator-tube comprising an oscillatorenergizingtransformer comprising an iron-core magnetic circuit with an air-gap init, a secondary winding connected as a plate-voltage source for saidoscillator-tube, and a primary winding, a discharging resistor shuntingsaid primary winding, means serially including said primary winding, asource of unidirectional voltage and a normally conducting control-tubefor energizing said primary winding, and control-means utilizing lessthan all of alternate half-waves of said low-frequency control-currentfor intermittently rendering said control-tube substantiallynonconducting, the secondary winding being connected to theoscillator-tube in such polarity that the oscillator-tube is oscillatingat approximately the same time that the control-tube is conducting, thetime-constant of the transformer being such that it will continue tochange its ilux during its discharge-periods when it is supplyingplate-circuit energy to the oscillator-tube.

BERNARD E. LENEHAN.

